Originally Posted By: Drew99GT
Originally Posted By: wolfc70
Originally Posted By: BumpDraft2004
And drawing in fresh air no less. You are brave.
That is a must in cold weather. If you recirculate the cabin air, you add moisture as the air warm up. Warmer air can hold more moisture, so the windows fog/ice up inside the car. By drawing in the cold, dry outside air, you keep the humidity level low, reducing the fog/ice.
The coldest was -39F in the later 1990's, it was in High School, and I was working late at night as a stocker for a store. Car was a 1988 Plymouth Reliant, with the 2.5. It started after sitting 7 hours in the cold, I had to jump 8 other employees that night. It was so cold that my jumper cables would not flex, it took two people to uncoil them. Coldest recently was -27F two winters ago.
I don't buy that for a minute! You don't add moisture just because the air temperature heats up - you add moisture from your breath! Warm air can hold more moisture at 100% relative humidity as your graph clearly shows - so if its colder, the chance of fogging windows increases! That's why you see fog and dew in the early morning when the temp is coldest and near the dew/frost point. You keep it off recirculate and crank the heater/defroster so the increased moisture from your breathing goes out of the cabin of the vehicle and the interior surfaces, to include glass, warm up past the dew/frost point and moisture won't condense/freeze on them.
Well, that is what I was trying to say. The added moisture is from you, snow melting off your boots/shoes, and many other ways. As the air temp increases, it can hold more moisture, that moisture than condenses on the cold glass. So in a way, you said what I was trying to say, so thanks!